The present invention relates generally to a drill, and in particular to a hammer drill.
Hammer drills are already known in the art. The are power-operated tools in which the drill bit can either be only rotated, or in which it can have axially acting blows superimposed upon its rotational movement. In some instances, these tools can also be switched so that only blows can be transmitted to the drill bit, that is the rotary motion can be switched off. In order to obtain the hammering action in these tools, it is known to mount the drive shaft which transmits motion to the drill bit for axial reciprocation, and to surround it with an impact member that is fixedly connected with the drive shaft and formed at one axial end with a plurality of circumferentially spaced projections. Adjacent this axial end is a stationary member which is fixedly mounted in the housing and which is formed with a further plurality of projections extending towards the impact member. The latter is urged by biasing means against the stationary component so that its projections will alternatively snap between those of the stationary component and be urged out from between them by the torque that is transmitted to the impact member. This transmits blows to the drive shaft which in turn transmits them to the drill bit.
It is evident that the projections of the stationary component and of the impact member will slide upon one another as they move into and out of interengagement. This sliding, in turn, causes friction which disadvantageously influences the effectiveness of these devices, aside from the undesired development of heat resulting from this friction. Added to these disadvantages of the prior-art constructions is a further one, namely the fact that relatively complicated mechanisms are necessary for moving their components to and from the hammer-drilling position.